Today’s whales share many anatomical traits with other mammals, but the unique adaptations of species such as Physeter macrocephalus, the sperm whale, illustrate how organisms can transform over time as they carve out their place on the planet. (A number of exhibits within the Whales: Giants of the Deep exhibition feature these large whales.)

Two sperm whale skeletons grace the exhibition Whales: Giants of the Deep

In fact, the bones of cetacean flippers are the same kinds of bones as in the human arm, with an upper arm bone, two forearm bones, and hand, wrist, and finger bones. In whales, fingers are elongated and may have additional bones. The joint between upper arm and forearm is immobile, creating an effective paddle.

Among sperm whales' (and other toothed whales') most amazing adaptations is echolocation, the use of sound to locate objects based on their echoes−and a way of navigating the world that is also used by some land mammals, including bats. The whales use this ability to, among other things, hunt successfully for deepwater prey, such as giant squid.

To create sound, the whale pushes air through one of its nasal passages to a pair of flaps that vibrate to create sound. The sound passes through the spermaceti organ (rendered in blue, top of the skull), bounces off an air sac, and is redirected to the whale's "melon" organ (rendered in yellow). Called "junk" by whalers, this organ contains fatty tissue that transmits sound, focusing the pulses in the process and allowing sperm whales to direct, or aim, sound waves.

The sperm whale's head is actually an oversized nose, which in mature males can make up a third of the animal's body. Sperm whales use their uniquely shaped nose to generate sound.

At the crux of the whale's jaw, the lozenge-shaped yellow portion (shown above, right) is the "acoustic fat pad." As echoes bounce back toward the sperm whale, they are received by this deposit of fat in the back of the whale's long, thin jaw. The sound is then transmitted through the ear bones.

A version of this story appears in the Spring 2013 issue of Rotunda, the Member magazine.

Whales: Giants of the Deep was developed and presented by the Museum of New Zealand Te Papa Tongarewa. This exhibition was made possible through the support of the New Zealand Government.

The American Museum of Natural History gratefully acknowledges the Richard and Karen LeFrak Exhibition and Education Fund.